Embryology of Reproductive System_PowerPoint

FC for second lecture on GYN US

what systems often have anomalies that coexist? why?

urinary system and reproductive system.

because urinary and reproductive systems develop alongside each other in embryo.

where do most congenital anomalies discovered before birth originate?

genitourinary system

although anomalies of the genitourinary system are induced early in embryonic development, when can they be detected…

not detected until long after birth (puberty and beyond)

what are Carnegie Stages?

a method used to classify the embryo.
categorizes the embryo, based on age, size, and morphologic characteristics.

how long do the Carnegie Stages last?

last through the first 8 weeks after conception/ of gestation

the 23 stages end after the 8th week when fetal period begins

when is chromosomal gender or sex determined?

at conception

the ovum always has what chromosome?

what does the sperm do (chromosome wise)?

when does this occur?

ovum always has the X chromosome.

sperm delivers either X or Y.

this occurs in pre-embryonic stage (Carnegie weeks 1-3; US weeks 3-5)

what is pre- embryonic stage?

period before embryonic disc rolls into tube—> BODY FOLDING!!

when do primordial germ cells appear?

• late 3rd/ early 4th week (Carnegie)— approx. 17 days after conception

where do primordial germ cells originate?

in yolk sac near allantois

what indicates the appearance of primordial germ cells?

primitive groove, primitive streak, node (from textbook- it says germ cells in PP.)

when does the intermediate mesoderm appear?

end of 2nd week of Carnegie Stage

week 4 US age

where do primordial germ cells migrate from—> to?

migrate from yolk sac along allantois and mesentery to urogenital ridge

what invades the genital ridge? what does this do?

primordial germ cells invade genital ridge

if germ cells don’t reach genital ridge, gonads won’t develop

what are primordial germ cells?

precursor of germ cells, become oocytes or spermatozoa in the adult.

explain the development of sex cords (generic, no specific gender attached)

• epithelial tissue grows into the mesoderm

• this forms the primitive sex cords

• PSC connect to the mesonephric duct

• gonad cannot be seen as male or female yet (called indifferent gonad)

For males, what chromosome pattern do the primordial germ cells carry? what gene is attached to this?

XY chromosome pattern.

SRY gene

what is the SRY gene? what does it do?

sex determining region on Y (of XY chromosome for males)

determines that gonads will be testis

causes tubules from mesonephric duct to penetrate genital ridge and stimulate further development of testis

SRY gene starts signaling process to induce the formation of what?

Sertoli and Leydig cells in testis

what do Sertoli cells do?

secrete Mullerian Inhibiting Substance (MIS) which causes the degeneration of of paramesonephric ducts (male fetus does not need them)

what do Leydig cells do?

secrete testosterone:

• testosterone causes development of Mesonephric ducts

• some testosterone converted to Dihydrotestosterone (differentiation of male external genitalia)

what does the tunica albuginea do after being formed?

separates testis from surface epithelium

what structures does the mesonephric duct form (males)?

epididymis, vas Deferens, seminal vesicles, and ejaculatory duct

what is the remnant of the paramesonephric ducts (males)?

appendix epididymis

how long do external genitalia (males) remain indifferent?

through the end of the 6 week fertilization age (Carnegie) (8th week US age)

note= even after 8 weeks sex determination is difficult, most would say 12 weeks.

what structures do the genital tubercles form (in males)?

•Genital Tubercle—> Phallus—> Penis

what structures do the urethral folds form (in males)?

•Urethral Folds—> lateral walls of Urethral Groove —> Urethral Plate—> Penile Urethra

what structures do the genital swellings form (in males)?

•Genital Swellings—> Scrotal Swellings—> Fuse to form Scrotum

what chromosome pattern do female primordial germ cells have? is there a specific gene attached to this? what do the genes of the X chromosome encourage?

XX

there is no Y chromosome so there is no SRY gene

ovary development

primitive sex cords (in females) form irregular clusters of cells where? what do these later become?

in center of ovary.

later are replaced by a vascular framework which becomes the ovarian medulla

surface epithelium of the primitive ovary (in the genital ridge), continues to grow and forms what?

new sex cords

cortical cords, which remain close to surface of ovary.

what happens to the mesonephric and paramesonephric ducts in female development?

•Mesonephric duct (important for male gonad growth) degenerates

•Paramesonephric duct (important for female gonad growth) proliferates

in ALL embryos, where does the paramesonephric duct originate?

urogenital ridge

in females what do the paramesonephric ducts form?

•Cranial, funneled end—> Infundibulum (Rt/Lt)

•Cranial vertical portion & horizontal mid part—> Fallopian Tubes

•Caudal vertical portions fuse—> Uterus, Cervix, Upper Vagina

what forms the broad ligament?

paramesonephric ducts cross towards midline and fuse

this forms a fold of peritoneum n the pelvis = broad ligament

the uterus and broad ligament divide the pelvis into:

anterior and posterior regions

• anterior: uterovesical pouch

• posterior: retrouterine pouch/ pouch of Douglas/ cul de sac

epoophoron aka:

organ of Rosenmuller

parovarium

what is the epoophoron

remnant of the mesonephric duct (which degenerate in the female)

where is the epoophoron found?

in broad ligament between fallopian tube and ovary

what is the paroophoron?

remnant of the mesonephric duct

where is the paroophoron found?

in broad ligament between epoophoron and uterus

epoophorons and paroophorons may be the source of…

paraovarian cyst or adenoma

the vagina is dual origin: where are the upper and lower portions derived from?

•Upper portion: caudal end of paramesonephric ducts (fused)—including Vaginal Fornices

•Lower portion: sinovaginal bulbs

what do the sinovaginal bulbs (in females) form?

vaginal plate

which way does the vaginal plate grow?

towards the uterus

what is the hymen?

thin membrane that is the remnant of the vaginal plate at junction where sinovaginal bulbs arose from urogenital sinus

what does the genital tubercle (in females) form?

clitoris

what structure do the urethral folds form (in females)?

labia minora

what structure do the genital swellings form (in females)?

labia majora

what structure does the urogenital groove form (in females)?

vestibule

by Carnegie stage 23 (end of 8th week), the external genitalia of males and females is…

completely formed (all parts are there), but not fully developed / not well enough seen on US to determine gender.

during which week of gestation does the germ cell migrate to the yolk sac?

5th week